Constructing Gas Lasers Inside of Photonic Band Gap Fiber Optic Cells

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Constructing Gas Lasers Inside of Photonic Band
Gap Fiber Optic Cells

• Joshua Perkins
• Texas AM University
• Kansas State University REU
• Mentor- Dr. Kristan Corwin

R. Thapa et al, Opt. Express, 2006
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Gas Lasers

• Well understood
• Relatively cheap gain medium
• Difficult to damage the gain medium
• Large volumes of active material
• Very Efficient
• Bulky
• Complex
• Fragile

Diode Laser http//en.wikipedia.org/wiki/ImageLas
er_diode_chip.jpg
http//technology.niagarac.on.ca/lasers/Chapter6.h
tml
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Outline

• How molecular gas lasers work
• Why we picked Acetylene gas
• How laser cavities work
• Our solution for better gas cells
• Our laser cavity setup and estimated losses
• My accomplishments this summer

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Optically Pumped Gas Lasers

• Pump
• Relaxation
• Stimulated Emission of Radiation

http//www.answers.com/topic/population-inversion-
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Detailed Model
... J12 J11 J10 J 9 ...
v1v3
N3

P13
... J12 J11 J10 J 9
v4
N2
... J13 J12 J11 J 10 ...
No Vibration
N1
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Rate equations
Abs.
Abs.
Stim.
Spon.
Spon.
Abs.
Stim.
Stim.
Spon.
Spon.
Abs.
Abs.
Stim.
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Gain
Alkali-vapor lasers can have gains of 2000x CO2
is about 4 per cm and up to 200 per centimeter
for pulsed CO2
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Acetylene Gas

• Well understood
• Quickly available
• Frequency reference measurements
• Possible to produce light in a region that works
  well with fiber optic equipment

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Laser Cavities

• A laser cavity is simply gain medium between
  mirrors with some way to get energy in and
  photons out.

Mirror
Mirror
C2H2
Glass Tube

• Issues
• For more gain a longer (or wider) cavity is
  required, but scaling is an issue
• Pump Beam Size
• Intensity in gain medium

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Fiber Optic Cell
Cross section of the smallest human hairs
Splice
Splice
SM Fiber
SM Fiber
PBG Fiber

• Much less fragile
• Flexible even during lasing
• Extremely high intensities compared to normal gas
  cells
• Input and output are fiber allowing for the use
  of other fiber optic devices.

• Splices between SMF and PBGF are hard to make and
  are lossy
• Loss is due to mode mismatching because PBG are
  multi mode and Single Mode are not. Also
  Refractive index Change
• Delicate due to fine structure being melted to
  the solid face of SM fiber

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Variable Pressure Cavity
To pump
Gas Inlet
Pump
Mirror
Hollow optical fiber
OC Mirror
Laser
Polarizing Beam Splitter
C2H2 molecules

• Has worked in the past
• Polarization is necessary because dichroic
  mirrors dont exist for these wavelengths
• More vacuums to maintain and more free space
  optics to align

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Output Coupler Vacuum Chamber
14cm
Screw
4cm
5cm
Curved Mirror
Bellows
5cm
Screw
Vacuum
XYZ Translation
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Final Setup
0.59 dB
7.11 dB Round-trip Loss
PBS
Fiber Mirror
0.83 dB
0.32 dB
R 99
1.87 dB
f 40 mm
2.9 dB (estimated)
f 25 mm
PD
PBGF
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Final Setup
Light from Decepticon (1532 nm) Amplified by an
EDFA
0.59 dB
7.11 dB Round-trip Loss
PBC
Fiber Mirror
0.83 dB
0.32 dB
R 99
1.87 dB
f 40 mm
2.9 dB (estimated)
f 25 mm
PD
PBGF
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What I have learned this summer

• Splicing Fibers
• Fiber Optic Components
• Free space optics
• Optically pumped gas laser theory
• Vacuum Systems

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What I have done this summer

• Design of optical and vacuum systems
• Part ordering
• Building of optical and vacuum systems
• Took a project that had just cleared the proposal
  stage and built a functional testing apparatus.

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C2H2
Buffer Gas
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Summary

• How molecular gas lasers work
• How laser cavities work
• Improvement of gas cells using PGB Fibers
• Vacuum chamber and fiber lasing scheme setup
• What I learned in the REU

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Future Directions

• Fluorescence Testing.
• Rate constant control with buffers
• Working all fiber gas laser
• Comparable to diode lasers for cost and size, but
  keeps the advantages of gas lasers

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Acknowledgements

• K-State REU Program 2008 funded by NSF
• Dr. Kristan Corwin Mentor
• Dr. Larry Weaver
• Andrew Jones
• Kevin Knabe
• Dr. Karl Tillman
• Mike Wells